1. Field of the Invention
The present invention relates to a zoom lens suitable to a digital camera, a video camera, or the like. More particularly, the present invention relates to a zoom lens including a macro mechanism that can obtain an excellent optical performance across an overall object distance.
2. Description of the Related Art
It is demanded for many photographic optical systems for use in image pickup apparatuses that a zoom lens is a zoom lens of a high zoom ratio as well as a zoom lens that can shoot an image of an object at a shorter distance at a high imaging magnification. As a focusing method for a zoom lens, an inner focus method is known in which focusing is performed by moving at least a single lens unit in an optical axis direction. The lens unit is disposed on the image side of a first lens unit disposed closest to an object side.
A zoom lens discussed in U.S. Patent Application Publication No. 2011/0116174 is a four-unit zoom lens including a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, and a fourth lens unit having positive refractive power, in which focusing is performed from an infinite distance to a short distance by moving the second lens unit toward the object side.
Moreover, to improve an aberration variation during focusing, a floating method is known in which a plurality of lens units is moved in the optical axis direction. See Japanese Patent Application Laid-Open No. 2000-047107.
Furthermore, a zoom lens including a macro mechanism is known. A zoom lens discussed in Japanese Patent Application Laid-Open No. 11-352402 can perform macro shooting by moving a first lens unit and a second lens unit in such a way that a distance between the first lens unit and the second lens unit is increased at a telephoto end.
In order that a zoom lens obtains a high optical performance in the entire zooming range and across an overall object distance (the entire focusing range), it is necessary to appropriately set the power and a lens configuration of each lens unit forming the zoom lens, and a zooming method and a focusing method constituting the zoom lens. Generally, when it is desired to shorten a photographable object distance and to increase an imaging magnification, it is likely to increase an aberration variation during focusing and to decrease optical performance. Moreover, such a problem arises in that the amount of movement of a focus lens unit is increased to upsize the zoom lens.
The zoom lens discussed in U.S. Patent Application Publication No. 2011/0116174 can achieve focusing at a some short distance in the entire zooming range, and about a 0.2× imaging magnification can be achieved at a shortest distance at a telephoto end.
It is necessary in the zoom lens discussed in U.S. Patent Application Publication No. 2011/0116174 that a space is secured in the optical axis direction by an amount of the movement of the second lens unit for focusing. Thus, it is difficult to obtain a high imaging magnification exceeding a 0.5× magnification while downsizing the entire zoom lens. Furthermore, since only the second lens unit is moved during focusing, an aberration variation is increased, and an aberration variation is likely to be increased particularly at the telephoto end.
Japanese Patent Application Laid-Open No. 2000-047107 discusses that a six-unit zoom lens includes a first lens unit having positive refractive power, a second lens unit having negative refractive power, a third lens unit having positive refractive power, a fourth lens unit having negative refractive power, a fifth lens unit having positive refractive power, and a sixth lens unit having negative refractive power. The fourth lens unit is moved toward the object side and the sixth lens unit is moved toward the image side so that focusing is performed from the infinite distance to a short distance. This technique can achieve focusing at some short distance in the entire zooming range, and can obtain an about 0.2× imaging magnification at a shortest distance at the telephoto end. During focusing, an aberration variation is decreased by moving the fourth lens unit in such a way that the fourth lens unit compensates aberration caused by the movement of the sixth lens unit. However, it is necessary to secure spaces in the optical axis direction by the amounts of the movement of the fourth lens unit and the sixth lens unit during focusing. Thus, it is difficult to obtain a high imaging magnification exceeding a 0.5× magnification while downsizing the entire zoom lens.
Japanese Patent Application Laid-Open No. 11-352402 discusses the zoom lens including a macro mechanism that can obtain a high imaging magnification of an about 0.5× magnification. However, a drive method for the lens units for macro shooting, for example, is not matched with the downsizing of the entire zoom lens and the providing of a high performance.